So far it seems like SS, FT, BS, DT are pretty consistent for me. IS and 123RF are quite liberal, I got above 50% acceptance rate. Only Crestock is way below my average.

In my experience BS has been the easiest of those you listed to get images accepted.  IS is my worst acceptance rate (48% last time I looked) of the sites where I actually make money.  StockXpert though is worse.  Not only do they reject tons for "sorry we're not looking for such images at this time", but their review times have slowed to a crawl.  My last batch has been sitting out there for two weeks now.

Anal reviewers I don't have a problem with.  Picky is good because it keeps the collections tight and forces us to have to up our game.

What drives me nuts are the occasional rogue (usually new) reviewers that show up and arbitrarily reject most or all of a batch with little or no explanation.   And when that happens it usually turns out to be a sitewide problem with lots of bewildered contributors left scratching their heads.

I have found DT, IS, and BigStock to have the most consistent reviews. 

Crestock - so much so that I have stopped uploading there.

Hear hear, Lisa! 

In the last few months, I was having problems at LO with rogue newbies, and that was with me being a reviewer there myself!  LOL  If the reviewing policy had changed, I sure as h*ll didn't get the memo!  I went more than a year without a single rejection, and then BOOM!!!  Poor lighting on a silhouette, using the keyword "isolation" on an object shot on white that had a barely noticeable shadow, focus problems on a panned shot of a moving vehicle, etc.  Man...I felt like all of a sudden I didn't know how to review my own photos anymore, much less anyone else's.  Incredibly frustrating to say the least.

SS seems to have the most over-eager-to-reject newbies.  My last batch was hit with the dreaded "Limited Commercial Value" blanket rejection again.  Just when I thought they'd fixed the problem.

DT and IS are the best.  Very rarely do I ever disagree with their rejections.   

For me StockXpert, hands down, wins the most anal reviewers award

IS by far rejects the most stuff.  I'd have to check my "Rejected" folders to know for sure, though.  Not sure who's in second place--probably FT.  For some reason StockXpert seems to like what I've been uploading, but we'll see when they get to what I uploaded the other night...  They're currently my best selling site this month, even surpassing SS.

IS, DT and SS are the most consistent for me - FT has become impossible - dropping from 50% to 5% acceptance.  BigStock & 123 are middling - some arbitrary rejections, but  mostly ok.  albumo & feature take almost anything [except for one reviewer at albumo who reject 100% of 2  large, varied submissions], but they dont sell anything so it hardly matters.

i was ready to give up on BigStock, 123 and FT, but sales have improved there over the last 3 mos so i'll still submit when i have time.   

s

FT rejects 60% of my shots (holding steady)
IS rejects 45% (getting better)
SS rejects 35% (holding steady, for some reason they don't think that I can focus my camera, all rejects in the last month have been for focus, never got a focus rejection elsewhere though, unsharpened vs. unfocused, can they tell the difference?)
BigStock rejects 20% (holding steady, they hate anything with DOF effects)
123RF rejects 15% (holding steady)
DT rejects 10% (I've got a 40 shot no reject streak going)